A variety of techniques are used to make high density circuit modules. Memory expansion is one of the many fields in which high density circuit board solutions provide space-saving advantages. For example, the well-known DIMM (Dual In-line Memory Module) board has been used for years, in various forms, to provide memory expansion. A typical DIMM includes a conventional PCB (Printed Circuit Board) with DRAM memory devices and supporting digital logic.
Strategies used to devise and/or increase the capacity of DRAM-mounted DIMMs may be applicable to other memory modules such as, for example, memory modules that employ flash memory storage or added memory for video processing. The module is typically mounted in the host computer system by inserting a contact-bearing edge of the module into a card edge connector. Typically, systems that employ memory modules provide limited space for such devices and most memory expansion boards are somewhat limited in the memory capacity they add to a system. There are several known methods to improve the limited capacity of a memory module. Such methods have various cost or performance impacts. Further, many capacity increasing techniques exacerbate profile issues and contribute to thermal management complexities.
One scheme to increase circuit board capacity is multiple die packages (MDP). This scheme increases the capacity of the memory devices on the module by including multiple semiconductor die in a single device package. The additional heat generated by the multiple die typically requires, however, additional cooling capabilities to operate at maximum operating speed. Further, the MDP scheme may exhibit increased costs because of increased yield loss from packaging together multiple die that are not fully pre-tested.
In yet another strategy, stacked packages are employed to increase module capacity. This scheme increases capacity by stacking packaged integrated circuits to, create a high-density circuit module. In some techniques, flexible conductors are used to selectively interconnect packaged integrated circuits. Staktek Group L.P. has developed numerous systems for aggregating leaded or CSP (chipscale packaged) devices in space saving topologies. The increased component height of some stacking techniques may alter, however, system requirements such as, for example, required cooling airflow or the minimum spacing around a circuit board on its host system.
Typically, the known methods for increasing memory module capacity raise thermal management issues. What is needed, therefore, are methods and structures for providing high capacity circuit boards in thermally efficient, reliable designs that perform well at higher frequencies but are not too large, yet can be made at reasonable cost with commonly available and readily managed materials.